Method for the recovery of tar acids by extraction in the presence of an alkali soluble hydrosulfite



2,724,001 Patented Nov. 15, 1955 ice METHOD FOR THE RECOVERY OF ACIDS BY EXTRACTION IN THE PRESENCE OF AN ALKALI SOLUBLE HYDROSULFITE Calvin Golumbic, Pittsburgh, Pa., assignor to the United States of America as represented by the Secretary of the Interior No Drawing. Application April 19, 1952, Serial No. 283,236

Claims. of. 260-627) (Granted under Title 35, U. S. Code (1952), sec. 266) The invention herein described and claimed maybe manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of royalties thereon or therefor.

This invention is concerned with an improved method for the recovery of tar acids.

In the recovery of tar acids from the products of the carbonization or the hydrogenation of coal or from petroleum and similar materials, the basic step in the recovery procedure is the extraction of the tar acid-containing material with an aqueous caustic solution. After extraction, the tar acids are sprung by acidification of the extract and then subjected to the usual purification procedures. Oftentimes, tar acids obtained by this procedure are highly colored and possess an undesirably high viscosity. Apparently, darkening and high viscosity are the result of side reactions occurring during the caustic extraction. These undesirable effects are particularly apparent in the recovery of tar acids from low temperature tars produced by the low temperature carbonization of coal, lignite, and the like. With this type of material, furthermore, serious loss of potentially recoverable tar acids often occurs owing to the precipitation of resinous, and insoluble material during the caustic extraction.

In accordance with the present invention, it has been found that undesirable side effects occurring during caustic extraction which often lead to darkening, increased viscosity, and diminished yields, can be substantially mitigated or entirely prevented by conducting the extrac tion in the presence of a relatively small amount of an alkali soluble hydrosulfite, preferably an alkali metal hydrosulfite such as sodium hydrosulfite, Na2S2O4. Most desirably, the alkali soluble hydrosulfite is addedto the aqueous caustic solution employed as the extractant which contains usually from 5% to 20% of a strong alkali such as NaOH or KOH. The amount of hydrosulfite required will depend upon the material being extracted, more or less being necessary depending upon the tendency of the material to undergo reactions which lead to darkening and other undesirable side effects. The minimum amount necessary in any particular case can be determined by simple experiment. In most cases, a relatively small amount of the order of .2% to 3% based upon the weight of the caustic solution employed as the extractant will be found satisfactory.

Alkali soluble hydrosulfites suitable for use in accord ance with the invention include, for example, alkali metal hydrosulfites such as sodium hydrosulfite Na2S2O4, potassium hydrosulfite K2S2O4, as well as ammonium hydrosulfite (NH4)2S2O4. Sodium hydrosulfite is to be preferred for its cheapness and availability. While the action of the hydrosulfites in preventing the undesirable effects discussed above is not completely understood, it is believed that these materials prevent the oxidation and subsequent polymerization of such compounds as dihydric phenols which are present in the mixture being extracted. It is to be understood however, that the invention does not depend upon this, or any other particular theory as to the ultimate explanation of the beneficial effects pro- While the efiicacy of the hydrosulfites is probably due at least in part to their reducing properties, it has been found that other similar reducing agents such as sodium sulfite, NazSO3, and sodium bisulfite, NaHSO3, are ineffectual in preventing the undesirable side effects of alkali extraction. These other relatively strong reducing agents such as sodium sulfoxylate HzCOHSO3Na, sometimes produce transient beneficial effects but after short storage periods the extracted products rapidly deteriorate, increasing in color and viscosity, and often the end result of the addition of these other compounds is actually deleterious rather than beneficial.

Example 1 A tar obtained by the low temperature carbonization of lignite was distilled into the following fractions:

Fraction, boiling range, C.

pitch Appearance of cresylate layer Fraction, boiling range, 0. i p Extraction with- Of N32520: out NaaSzOl 150200 colorless..." reddish brown. 200-250 do deep red-brown. ZEN-300. .do Do. 300350- yellow dark brown. 350-400 -do Do.

Similar extraction tests using sodium sulfite NazSOz, sodium bisulfite NaHSOz, and sodium sulfoxylate HzCOHSOsNa were conducted. Although the cresylates initially obtained were somewhat lighter in color than those obtained with a straight caustic solution, darkened rapidly on standing and dark precipitates indicating reaction of the reducing agent with substances present in the cresylate.

Example 2 A distillation fraction boiling between 150 and 300 C. of a tar obtained from the low temperature carbonization of lignite was extracted with an aqueous solution of 5% KOH containing 1% Na2S2O4. A similar fraction was extracted with a 5% aqueous solution of KOH Without any added hydrosulfite. In each case, the alkaline extract was back washed with benzene, acidified with dilute sulfuric acid, and the tar acids recovered by extraction with ether. a v

The tar acids extracted by the caustic solution containing added Na2S2O4 were light yellow in color, and did not darken upon standing. The acids extracted in the absence of NazSzOr were reddish brown in color, and became progressively darker upon storage.

7 solid .sodium bicarbonate .for several hours. ture was filtered, and the filtrate divided into two portions. One portion was treated with an aqueous solution Y readily,

Example 3 A distillation fraction boiling between 300 and 400 C. of a tar obtained from the low temperature carbonization of lignite was'refluxed in a benzene solution over The mix- KOH and 1% NazSzOt, and the :other The containing with 5% KOH withoutthe addition of Na2S204.

V, tar acids were recovered from the alkaline extracts by acidifiation of .the extracts With dilute sulfuric acid and extraction ether.

During the caustic extraction, the portion extracted in the presence of NazSzOrz underwent phase separation both phases during the extraction were light in color, and there was no perceptible precipitation. During the extraction in the absence of added NazSzO4, both phases were dark and'noticeab'le precipitation of insoluble material occurred. The tar acids extracted in the presence of added NazSzOr were recovered as a mobile liquid of relatively low viscosity, while those extracted without the addition of NazSzOr had an undesirably high viscosity.

Example 4 The tar acids produced in Examples 2 and 3 by extraction in the presence of sodium hydrosulfite were combined and distilled to a vapor end point of 210 at mm. The ta-r acids produced in Examples 2 and 3 by extraction'without the use of sodium hydrosulfite were combined and distilled in a similar manner. The distilled tar acids which had been extracted in the presence ofisodium hydrosulfite were light in color and did not darken after several weeks storage. The tar acid'distillate which had been extracted without the use of the "hydrosulfite was initially darker in color and became progressively darker upon storage. Example 5 Several fractions from a coal hydrogenation oil produced by the hydrogenation of a bituminous coal under a pressure of 7500 pounds per square inch and .at a tem- F. were extracted with an aque- .perature of about 850 ous solution containing 10% sodium hydroxide and 2% by Weight of sodium hydrosulfite. Similar fractions were extractedwith a 10% sodium hydroxide solution without added sodium hydrosulfite. After phase separation, the cresylatelayer was inspected for coloration. The following results were obtained:

: Appearanceof cresylate layer 'Fractlon,boiling;range,F. V, Extraction Egtmcmn with gg gyg out NerSzO:

s1-3so j ellow".-- brown. 210452 amber darkbrown.

o black opaque.

aim-645 c ams fite during the extraction step the high or low temperature caris particularly useful in connection with the recovery of tar acids from the products of the low temperature carbonization of coal, especially from the low temperature carbonization products of the lower rank coals such as lignite. These low temperature tars apparently contain a greater amount of material which undergoes undesirable side reactions during caustic extraction than do high temperature tars.

If desired, other precautions may be taken in addition to the use of the alkali soluble hydrosulfite to prevent undesirable side effects during the caustic extraction. For example, by conducting the extraction in an oxygenfree atmosphere, further improved results can be obtained.

By operation in accordance with the invention, the final tar acid products are usually recovered in greater yields and are often substantially improved in marketability. They are generally colorless or only slightly colored, and of low viscosity, whereas those produced in accordance with conventional procedures are often opaque .or highly colored, and of relatively high viscosity. These improvements :are obtained without introducing an additional stage in .present tar refinery practice, and with the use of only small amounts of a relatively inexpensive reagent.

It is to be understood that the above description, together with the specific examples and embodiments described, is intendedmerely to illustrate the invention, and that the invention is not to be limited thereto, nor in any way except by the scope of the appended claims.

I claim: I

.l. .A method for recovering ta-r acids from materials selected from the group consisting of coal carbonization products and coal hydrogenation products which comprises extracting said products with an aqueous caustic solution containing from 2% to 3% of sodium hydro- .sulfite.

2. A method for recovering tar acids from the products of the low temperature carbonization of coal which comprises extracting said products with an aqueous caustic solution containing from .2% to 3% ,of sodium hydrosulfite.

3. A method'for recovering tar acids from aproductso'f the low temperature icarbonization of lignite which comprises extracting said products -with an aqueous caustic :solution' containing from .2% to 3% sodium .hydro- .sulfite.

-4. A method for recovering tar acids from materials selected from the group consisting of coal carbonization products .and coal hydrogenation products whichcomprises extracting said products with an aqueous caustic solution containing trom 0.2% to 3% of sodium hydrosulfite, acidifying the causticsolution with a weak mineral .acid, and extracting the resulting tar phase with ether. 5. A method for recovering tar acids from the .materials selected from the group consisting of .coal carbonization products and coal hydrogenation products which comprises extracting said products with an aqueous caustic solution containing from 0.2% to 3% of a compound selected from the group consisting of the hydrosulfites-of sodium, potassium, and ammonium, acidifying the caustic solution with .a weak mineral acid, and extracting .the resulting solution with ether. 7

References Cited in the tile of this patent UNITED STATESPATENTS 

5. A METHOD FOR RECOVERING TAR ACIDS FROM THE MATERIALS SELECTED FROM THE GROUP CONSISTING OF COAL CARBONIZATION PRODUCTS AND COAL HYDROGENATION PRODUCTS WHICH COMPRISES EXTRACTING SAID PRODUCTS WITH AN AQUEOUS CAUSTIC SOLUTION CONTAINING FROM 0.2% TO 3% OF A COMPOUND SELECTED FROM THE GROUP CONSISTING OF THE HYDROXULFITES OF SODIUM, POTASSIUM, AND AMMONIUM, ACIDIFYING THE CAUSTIC SOLUTION WITH A WEAK MINERAL ACID, AND EXTRACTING THE RESULTING SOLUTION WITH ETHER. 